The technical field of this disclosure is lighting control, particularly, electronic switching and control for a bi-level fluorescent lamp fixture.
Bi-level switching of fluorescent lamps allows space to be illuminated as needed by providing a high level of illumination when the space is occupied and a lower level of illumination when it is not. This can be accomplished by lighting all of the fluorescent lamps for high level illumination and lighting some of the fluorescent lamps for lower level illumination. Energy use and energy cost will be reduced if lights are switched off for lower level illumination. The illumination level can be controlled manually, with timers, or with sensors able to detect when the room is occupied.
Bi-level switching of fluorescent lamps has been accomplished using a triac to switch power at the ballast output, but using a triac does not allow continuous lighting. Such switching is described in U.S. Pat. No. 5,808,423 to Li et al., assigned to the same assignee as the present invention and incorporated herein by reference. The ballast must be switched off between the high power level of the high level illumination and the low power level of the lower level illumination because the triac remains latched until power is removed completely. This is inconvenient to the occupants, since the light is switched off to switch from high to low level illumination. It is also confusing to the occupants, because the bi-level lighting is operated from a single switch. In addition, switching decreases the useful life of the lighting components, because of the input current surge when switching levels. Bi-level operation could be provided using an individual ballast for each group of fluorescent lamps, but this would be costly.
One difficulty is to maintain approximately the same light level on all the lamps during high level illumination and be able to drop the input power to 50% during low level illumination. Designs using unequal light level between lamp groups have been used, so that the lower power lamps are driven at 50% input power when the higher power lamp group is off, but the unequal brightness level provided in this approach is not commercially attractive.
It would be desirable to have electronic switching for a bi-level fluorescent lamp fixture that would overcome the above disadvantages.
One aspect of the present invention provides electronic switching for a bi-level fluorescent lamp fixture.
Another aspect of the present invention provides electronic switching for a bi-level fluorescent lamp fixture without the need to power off the ballast during switching.
Another aspect of the present invention provides electronic switching for a bi-level fluorescent lamp fixture allowing bi-level operation to reduce energy use and expense.
Another aspect of the present invention provides electronic switching for a bi-level fluorescent lamp fixture allowing bi-level operation using a single ballast per light fixture.
Another aspect of the present invention provides electronic switching for a bi-level fluorescent lamp fixture that avoids decreasing the useful life of lighting components.
Another aspect of the present invention provides approximately the same light level from all lamps during high level illumination and reduces input power during low level illumination.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof.